| Along with the increase of the population and the development of the urbaneconomy, the resources of the land are lacking more and more. The method of polderreclamation, which can efficiently solve the problem of the resources of the land, wasrapid development. The undersea silt what is as the major hydraulic filling materialcannot satisfy the needs of general engineering due to its high moisture content, highabsorbance, high void ratio, low permeability and low strength. There is a commonlyused method that resting the silt for about one or three years and letting it naturesettlement. Then reinforce the silt when it has a certain bearing capacity. But themethod above causes the enormous waste of time and economic. Therefore, how toaccelerate the consolidation of silt become an urgent problem.The method that hydraulic filling the silt while consolidating it puts forward anew train of thought for accelerating the consolidation of dredger fill. This methodcan shorten the construction period effectively. But during the time of the drainageand the consolidation, a few of tiny particles will jam the drainage channels under theexcess pore water pressure. Finally there will form a mud membrane on the drainageplate. Therefore, the mud membrane will stop the further drainage and seriously affectconsolidation effect. Hence, in order to make a efficient drainage in a proper time, thefisht problem, which is need to solve, is to fully understand the settlement process ofthe silt under its weight and the formation of the microstructure. Study this topic cando a theoretical discussion on the problem and guide the current engineering practice.At the same time, this topic will be a new subject of the form of the soil.This thesis had done a number of simulating lab tests for the advance consolidation of dredger fill only owing to the time limit and take the soil sample ofthis phase for mercury injection experiment. Then acquired the shearing strength, thestereoscan photographs and the pore distribution of dredger fill during consolidationfor the subsequent drainage experiment.A. The research objectives of this thesis:This paper had got the basic physical and chemical property of dredger fill by theconventional experiments. Then got the change rule of pore diameter and shearingstrength of dredger fill during consolidation by mercury injection experiment andvane shear test. Finally simulated the process of consolidation, then tried to describethe generation and collapse of pore.B. The detailed experimentation:a). This paper had made the granularity analysis, mineral analysis, soluble saltdetermination, cation exchange capacity determination on the dredger fill that gotfrom Tianjin Binhai new area, then obtained the basic property of dredger fill such asthe grain classification, the mineral composition, the content of organic matter andsoluble salt.b). This paper had taken the dredger fill samples with high moisture content bythe homemade sampler, then carried the mercury injection experimental research.(The sampler can quick freeze the dredger fill as original state by liquid nitrogen.) Thevariation of moisture content and the porosity of the dredger fill had been acquired,the proportions of pore at each pore diameter level had also been worked out.c). The photographs for the samples had been taken by electron microscope, sothat the pore diameter can be intuitively observed. Then compared the dates ofmercury injection experiment and the photographs and analyzed the variation of poreat each pore diameter level. Then drew the trend line of pore variation in detail.d). In each time point, the shearing strength of dredger fill had been measured bythe multiscale vaneshear apparatus which was developed by my tutor and me. Thetrend line of shearing strength had also been worked out. Then this paper comparedthe variations of pore and shearing strength, analyzed the relationship between thepore in microcosmic and the strength in macroscopic. C. Data processing and Process Simulation.a). The conventional experiments had been finished. With the granularityanalysis, mineral analysis, soluble salt determination, cation exchange capacitydetermination for the dredger fill, the following conclusions were obtained.1). The dredger fill that got from Tianjin Binhai new area was defined as siltyclay, mid plasticity.2). The mineral composition is formed with primary minerals primarily andsecondary mineral secondarily.3). The soluble salt is formed with sodium salt and chloride salt primarily, sulfatesecondarily and others rarely.b). This paper had drawn the trend line of shearing strength variation. In the pastresearch we had known that the dredger fill initial consolidation has two stages. Thefirst stage is free subsicence, and the second one is self-weight consolidation. Theinflection point of trend line will show the time demarcation point of these two stages,and the time quantum when shearing strength rapidly increased will also be got.c). This paper obtained the pore variation of dredger fill by the mercury injectionexperiment on samples. The pore had been divided into4groups by its diameter:>32μm,32μm～6μm,6μm～0.5μm,<0.5μm. In the first few hours, the proportion ofpore with>32μm diameter is over70%. Then according to the time lapse, in the first32hours, the proportion of pore with>32μm diameter had quickly dropped into44.43%, the proportion of pore with32μm～6μm diameter had grown into36.83%,and peaked in296hour, then started falling. The proportion of pore with6μm～0.5μm diameter was nearly unchanged throughout the whole test period, and theproportion of pore with <0.5μm diameter had kept increasing in the whole test period.d). With the photographs taken by electron microscope, the arrangement of soilgrain had been obtained. This paper compared the photographs and the pore diameterdata, then tried to find out the relationship between these two variations. In the firstfew hours, the soil gain structure had quickly formed, and then the smaller gains hadbeen adsorbed towards the larger gains, and the left space by adsorption was theoriginal pore. e). Under the data obtained by experiments, this paper simulated the process ofconsolidation by the software PFC2D. Compared the simulation result and the realcondition, and the result was in agreement with the experiment. |
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